Flexible printed circuit (FPC) is a printed circuit made of polyimide or polyester film as a substrate and having a high reliability and excellent flexibility. With the rapid development of microelectronic technology, the printed circuit board has been developed fast in the direction of multi-layer, lamination, functionalization and integration, which causes a large-scale adoption of micro-hole, narrow pitch and fine wire in the design of the printed circuit for the conception and design of circuit diagram. FPC will be increasingly widely used due to having a special function and will become a trend in the printed circuit board in the future. It is technically great difficult to manufacture the flexible printed circuit board, the conventional vertically electroplating process can no longer meet the technical requirements for high quality and reliability of interconnected holes, and therefore horizontally electroplating has been developed. At present, the supplement of copper ions to an acid-copper system in the horizontally electroplating in FPC industry mainly depends on copper oxide powder. However, the copper oxide powder required in this process must have a high activity and can be rapidly dissolved in the electroplating solution system.
Many scientific and technical literatures and patents involve methods for preparing copper oxide. The conventional method for preparing copper oxide may include: reacting a soluble copper salt, such as copper sulfate, copper nitrate and the like, with a precipitant, such as sodium carbonate, sodium bicarbonate and the like under a temperature, converting the soluble copper salt into solid basic copper carbonate, which is washed, calcined and decomposed into copper oxide. The conventional method of preparation, due to high content of impurities in copper source, is not adaptable to the requirements of current advanced FPC electroplating.
Chinese invention patent application No. 201410550840.5 discloses a method for preparing activated copper oxide powder comprising using a copper plate as a raw material, preparing a copper-ammonia complex solution through ammonia leaching process, followed by a fine filtration and evaporation under slightly negative pressure to give basic copper carbonate, which then was calcined at a low temperature to give activated copper oxide powder product. The copper oxide prepared by the method has characteristics of high activity and high purity of the product. However, the method, making no comprehensive circulation and utilization of introduced agents, has a high production cost and lacks competitiveness on the market.
Chinese invention patent application No. 201210068019.0 discloses a method for preparing copper oxide by dissolving copper, including: adding copper, ammonia water, and powdery ammonium bicarbonate or ammonium carbonate or a mixture of ammonium bicarbonate and ammonium carbonate into a reaction vessel, stirring continuously while introducing air or oxygen to conduct the reaction, and at the same time, disposing a circulating device to retransfer ammonia gas and carbon dioxide volatilized from the reaction vessel into the reaction vessel after recycling so as to get into the reaction; the reaction ended when the pressure of the system no longer changes as the temperature of the system increases, the undissolved copper in the reaction system was removed, the reaction solution was filtered, and the filter cake was retained, washed and calcined at a temperature of 500° C.-700° C. to give copper oxide. In the method, ammonia gas and carbon dioxide produced during the decomposition of ammonium bicarbonate when copper is dissolved in ammonia bicarbonate are recycled and utilized, but the method for recycling the same utilizes the absorbent to absorb a volatile gas and then the absorbent is heated so that the volatile gas escapes. Such a circulation and utilization process requires reheating and energy consumption, and does not meet the requirement for environment protection. In addition, the copper-ammonia complex solution formed after dissolving copper further contains lots of ammonia and carbon dioxide, which are not recycled and utilized in the method, and the filtrate containing copper ions and a small amount of ammonia is directly drained off as waste water. This is wasteful and applies great pressure on the environment protection.